The present invention relates to the preparation of a lactam-magnesium compound which is useful as a catalyst for anionic lactam polymerization.
It is well known that the anionic polymerization process proceeds most effectively when initiated with a strong basic catalyst. Suitable basic catalysts can be chosen from among a large variety of materials; for example, lactam-metal-containing compounds having an alkali metal atom bound to the nitrogen atom. One particularly useful class of these lactam-metal-containing materials are lactam-magnesium compounds such as capro-lactam magnesium bromide.
Heretofore, these lactam-magnesium compounds have been prepared either by a process which requires heating of the lactam monomer and the organomagnesium material at elevated temperatures for an extended period in order to melt the lactam monomer, or by dissolving the lactam monomer in a solvent. These procedures are not without attendant difficulties. For example, heating of the lactam at an elevated temperature increases the probability that the lactam monomer will polymerize. Moreover, even when the process is successfully carried out, the catalyst product generally requires further mechanical processing such as grinding prior to use. Although dissolving the lactam monomer in a solvent prior to reaction with the organomagnesium-containing material saves energy because the need for heating of the lactam monomer to melt it is alleviated, the catalyst product still requires mechanical processing prior to use.
There is a need, therefore, for an improved method of preparing anionic polymerization catalysts which is simple, efficient, and economical and results in a product which can be utilized without mechanical processing prior to use.